NEW YORK (Reuters Health) - A set of conditions known to accompany or portend type 2 diabetes, including obesity and high blood sugar, could more than double a person's risk of developing heart disease, according to a new study.

Further, the findings suggest that these factors can even work their negative influence in the absence of full-blown diabetes.

"We are in the midst of an obesity epidemic that is contributing to an increase in the number of people with the metabolic syndrome in North America," senior researcher Dr. Mark Eisenberg of McGill University, in Montreal, noted in an email to Reuters Health. "Thus, an increasingly large number of people are at a high cardiovascular risk."

About a quarter of North Americans are affected by the metabolic syndrome -- a cluster of at least three of the following cardiovascular risk factors: obesity, high blood pressure, high blood sugar, high levels of "bad" LDL cholesterol and low levels of "good" HDL cholesterol.

Many people with the metabolic syndrome have, or are on their way to developing, type 2 diabetes.

The use of this confluence of risks as a predictor for heart disease is an area of debate. Does its influence exceed the sum of its individual components? Some experts have suggested that the metabolic syndrome's ties to diabetes alone are enough to explain any purported link.

Before trying to address this ongoing debate, said Eisenberg, "we felt it was important to determine how much the metabolic syndrome increases someone's cardiovascular risk."

So he and his colleagues evaluated the evidence to date; they reviewed 87 studies, which included a total of nearly one million patients.

Overall, the researchers found that the metabolic syndrome increased the risk of cardiovascular disease, heart attack and stroke by two-fold or more. Patients with the syndrome also had a 50 percent increased chance of dying from any cause, they report in the Journal of the American College of Cardiology.

The harmful effects of the metabolic syndrome appeared stronger in women compared to men, and held up even in the absence of type 2 diabetes.

"We still do not fully understand how this risk differs between men and women or how much of the risk associated with the metabolic syndrome can be explained by the individual cardiovascular risk factors," noted Eisenberg.

Dr. Todd Brown of the University of Alabama, Birmingham, noted that even if the risk from metabolic syndrome proved not to be greater than the "sum of the parts," it would still be a "useful construct to understand."

"It emphasizes to clinicians and patients that these diseases are not isolated entities that have nothing to do with each other," he told Reuters Health in an email, adding that it also points to a "universal" approach to treatment and prevention.

"Of the five components of metabolic syndrome, obesity usually starts it off, followed by the development of the other four components," he added. "If you can decrease obesity, the other four tend to get better."

Nathan Wong of the University of California, Irvine, and president of the American Society for Preventative Cardiology, agreed. "The metabolic syndrome concept motivates us to treat the condition and its components together to ensure best quality of care and future prevention of the known cardiovascular consequences," he told Reuters Health in an email.

Eisenberg's team points to some limitations in their review, including inherent weaknesses in the studies they included. Many were observational in nature, for example, which hindered their ability to identify true cause and effect.

Nonetheless, the prevention and reduction of the metabolic syndrome "is essential to reduce cardiovascular disease and to save lives," Eisenberg said, pointing to the value of regular check-ups and lifestyle modifications, such as diet and exercise.

"Ultimately, population-level interventions such as New York City's ban on trans-fats," he added, "are needed to decrease the number of people with the metabolic syndrome and their corresponding cardiovascular risk."